1. Summary of the Invention:
The present invention relates to a mechanically set liner hanger assembly for the setting within a subterranean oil or gas well of a length of casing (commonly referred to as "the liner") in the well prior to cementing the liner within the well.
2. Description of the Prior Art:
Hydraulically activated liner hangers are well known, but also have some disadvantages. In hydraulically set hanger assemblies, pressure build-ups immediate some of the functionally interengagable parts are not easily detectable at the surface of the well. These build-ups normally are caused by hydraulic action or "shock" down hole which will prematurely shear a seat, remove a ball off of its seat, or the like, so that pressure within the tool is not sufficient to hydraulically activate the setting mechanism.
Commercially available mechanically set liner hangers have utilized spring mechanisms and a "J" mechanism to set the tool. When setting the liner in an extremely deep well, as well as in operations requiring considerable reciprocation of the drill pipe, continued frictional contact of the springs with the internal casing surface will cause the spring mechanism to wear out heavily, which may result in failure of the liner hanger assembly to properly set within the casing at the desired location.
Prior art mechanically set liner hangers provide the setting mechanism as an integrable part of the hanger assembly, the hanger assembly and the setting mechanism being left in the hole after the cementing process. This setting mechanism consists of the springs and a "J" slot mechanism. Since available space between the O.D. of the liner hanger and the I.D. of the casing is usually considerably restricted, the fragile spring assemblies are easily damaged. Additionally, the amount of drag available for activating the "J" slot mechanism is limited and difficulty is sometimes experienced in setting the liner hanger. Accordingly, the present invention overcomes this disadvantage by incorporating a drag mechanism and a "J" slot assembly within the running tool itself to provide space to use a drag block mechanism as opposed to a spring mechanism. Additionally, because the setting mechanism is comparatively expensive, it is now retrievable from the well since it is within the running tool, as opposed to being part of the hanger assembly, and can be repeatably utilized innumerable times.
Many commercially available mechanically set liner hanger assemblies utilize a series of circumferentially extending, longitudinally protruding elongated spring-like mechanisms which produce a drag on the hanger assembly as it is shifted longitudinally within the well bore for inter-relation with and operation of the "J" slot assembly to activate and set the hanger. The present apparatus utilizes a plurality of drag "block" mechanisms, as opposed to the circumferentially extending longitudinally protruding prior art spring assemblies. While spring assemblies can effectively carry only a minimum of sets of slips, the utilization of the present drag block assembly permits adaptation for effective use with multiple sets of slips. Additionally, the present invention provides a drag block mechanism which provides one unitized setting assembly incorporating the drag blocks as well as the "J" mechanism. Moreover, it should be noted that the present drag block mechanism does not swivel with respect to the conical pad elements and slip assembly. However, the conical pad elements and slip assembly are free to swivel with respect to the drag block assembly when the drill pipe is rotated during the hanger setting operation. The stationary position of the drag block assembly during drill pipe rotation prevents excessive wear on the exterior of the drag block mechanism which, in turn, permits longer life and assures reliability of the drag block mechanism.
Commercially available mechanically set liner hanger assemblies may not provide means for fail safe setting in the event of excess rotation of the drill pipe. The present invention overcomes this disadvantage by providing means which, after a predetermined number of right-hand rotations of the drill pipe, automatically sets the liner hanger within the well, so that the hanger does not fall to the bottom of the hole.
Many prior art mechanically set liner hanger assemblies provide slip mechanisms which are circumferentially off-set from the cone mechanisms therefor because one of the mandrels carrying the cones or the slips is free to rotate with the drill pipe. Rotation of the mandrel carrying the slips or the cones is required for the slips to become aligned longitudinally with the cones. The present invention overcomes this obstacle by providing a setting mechanism which requires only vertical movement of the conical pads relative to the slips, thus affording utilization of wider conical pads and slip mechanisms and, in turn, affording greater weight carrying capability to the hanger.
In many presently available liner hanger assemblies, the pumping of the cement slurry down the drill pipe and through the interior of the apparatus results in a greater pressure on the outside of the setting tool than that on the inside of the setting tool which results in a differential pressure across the particular component of the apparatus and enables a slurry flow to come between the hanger and the running tool. This can cause cement contamination around some parts of the hanger assembly as well as disengagement of a wiper plug assembly connected by a conventional shear pin to a mandrel, and/or greatly damage the elastomeric wiper cup assembly itself. The present invention overcomes this obstacle by providing a side seal assembly to resist such a slurry flow between the hanger and the running tool, and which is also operational upon picking up of the drill pipe during the sequence in releasing the running tool from the hanger to provide a check means for detecting release of the running tool from the hanger. During the releasing sequence, the weight indicator at the surface of the well might not indicate that the setting tool is released from the liner hanger because there would not be reflected thereon sufficient weight variation. Accordingly, the drill pipe rams are closed and pressure within the drill pipecasing annulus is increased while the drill pipe carrying the running tool is pulled during retrieval of the running tool from the hanger. A pressure drop within the drill pipe-casing annulus signifies that the side seal has become unseated in its bore within the hanger and is now positioned immediate the upper end of the hanger. Since the side seal is carried on the running tool, the positioning of the side seal out of its normal position within the bore will indicate disconnection of the running tool from the hanger.
Prior art liner hanger assemblies have utilized wiper plug assemblies to wipe cement clean from the casing by utilizing a shear pin mechanism which affixes the wiper plug to the running tool. During many operations, the drill pipe will be picked up or lowered and pressure surges may be trapped to create a pressure differential which will shear the shear pin affixing the wiper plug to the running tool. Accordingly, the wiper plug is enabled to free flow to the bottom of the well and is caught within the float shoe or other mechanism at the bottom of the liner. Since the wiper plug is thereby dropped, it is not available to operationally associate with the cement plug which is pumped down the drill pipe ahead of the circulated drilling fluid. Accordingly, completion of the cementing operation cannot be detected at the well surface. The present invention overcomes this obstacle by providing a wiper plug assembly which is held onto the running tool by a mechanism which is operationally pressure insensitive and which permits pressure equalization therearound so that pressure surges are unsuccessful in releasing the wiper plug from the running tool.